Gas turbine combustor and operating method thereof

ABSTRACT

A gas turbine combustor has a combustion chamber into which fuel and air are supplied, wherein the fuel and the air are supplied into said combustion chamber as a plurality of coaxial jets.

This is a continuation-in-part (CIP) application of U.S. Ser. No.10/083,360 filed Feb. 27, 2002, now pending, the entire disclosure ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a gas turbine combustor and anoperating method thereof.

2. Description of Prior Art

The present invention specifically relates to a low NOx type gas turbinecombustor which emits low levels of nitrogen oxides. The prior art hasbeen disclosed in Japanese Application Patent Laid-Open Publication No.Hei 05-172331.

In a gas turbine combustor, since the turndown ratio from startup to therated load condition is large, a diffusion combustion system whichdirectly injects fuel into a combustion chamber has been widely employedso as to ensure combustion stability in a wide area. Also, a premixedcombustion system has been made available.

In said prior art technology, a diffusion combustion system has aproblem of high level NOx. A premixed combustion system also hasproblems of combustion stability, such as flash back, and flamestabilization during the startup operation and partial loadingoperation. In actual operation, it is preferable to simultaneously solvethose problems.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a gas turbinecombustor having low level NOx emission and good combustion stabilityand an operating method thereof.

The present invention provides a gas turbine combustor having acombustion chamber into which fuel and air are supplied, wherein thefuel and the air are supplied into said combustion chamber as aplurality of coaxial jets.

Further, a method of operating a gas turbine combustor according to thepresent invention is the method of operating a gas turbine combustorhaving a combustion chamber into which fuel and air are supplied,wherein the fuel and the air are supplied into said combustion chamberas a plurality of coaxial jets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram, for explanation, including a generalcross-sectional view of a first embodiment according to the presentinvention.

FIG. 2 is a sectional view, for explanation, of a diffusion combustionsystem.

FIG. 3 is a sectional view, for explanation, of a premixed combustionsystem.

FIG. 4(a) is a sectional view of a nozzle portion of a first embodimentaccording to the present invention.

FIG. 4(b) is a side view of FIG. 4(a).

FIG. 5(a) is a sectional view, for detailed explanation, of a nozzleportion of a second embodiment according to the present invention.

FIG. 5(b) is a side view of FIG. 5(a).

FIG. 6(a) is a sectional view, for detailed explanation, of a nozzleportion of a third embodiment according to the present invention.

FIG. 6(b) is a side view of FIG. 6(a).

FIG. 7(a) is a sectional view, for detailed explanation, of a nozzleportion of a fourth embodiment according to the present invention.

FIG. 7(b) is a side view of FIG. 7(a).

FIG. 8(a) is a sectional view, for detailed explanation, of a nozzleportion of a fifth embodiment according to the present invention.

FIG. 8(b) is a side view of FIG. 8(a).

FIG. 9(a) is a sectional view, for detailed explanation, of a nozzleportion of a sixth embodiment according to the present invention.

FIG. 9(b) is a side view of FIG. 9(a).

FIG. 10 is a sectional view, for detailed explanation, of a nozzleportion of a seventh embodiment according to the present invention.

FIG. 11 is a sectional view, for detailed explanation, of a nozzleportion of an eighth embodiment according to the present invention.

FIG. 12 is a sectional view for detailed explanation of a nozzle portionof a ninth embodiment of the present invention;

FIG. 13(a) is a sectional view for detailed explanation of anothernozzle portion of the ninth embodiment of the present invention;

FIG. 13(b) is a side view for detailed explanation of a nozzle portionof the ninth embodiment of the present invention;

FIG. 14 is a sectional view for detailed explanation of a nozzle portionof the ninth embodiment of the present invention;

FIGS. 15(a)-15(f) are views for detailed explanation of various nozzleformations of the present invention;

FIG. 16(a) is a aide view for detailed explanation of a nozzle portionof a tenth embodiment of the present invention;

FIG. 16(b) is a side view for detailed explanation of another nozzleportion of the tenth embodiment of the present invention; and

FIG. 17 is a graphical illustration showing a relationship betweenpremixing distances and NOx emission amounts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, two kinds of combustion systems for a gas turbine combustor willbe described.

(1) In a diffusion combustion system, as shown in FIG. 2, fuel isinjected outward in the vicinity of the outlet of an air swirlerarranged at a combustor head portion so as to intersect with a swirlingair flow, generating a circulating flow on the central axis, therebystabilizing a diffusion flame.

In FIG. 2, air 50 sent from a compressor 10 passes between an outercasing 2 and a combustor liner 3, and a portion of the air flows into acombustion chamber 1 as diluting air 32 which promotes mixture ofcooling air 31 and combustion gas in the combustor liner, and anotherportion of the air flows into the combustion chamber 1 through the airswirler 12 as head portion swirling air 49. Gaseous fuel 16 is injectedoutward from a diffusion fuel nozzle 13 into the combustion chamber 1 soas to intersect with the swirling air flow, and forms a stable diffusionflame 4 together with the head portion swirling air 49 and primarycombustion air 33. Generated high-temperature combustion gas flows intoa turbine 18, performs its work, and then is exhausted.

The diffusion combustion system shown herein has high combustionstability, while a flame is formed in a area in which fuel and oxygenreach the stoichiometry, causing the flame temperature to rise close tothe adiabatic flame temperature. Since the rate of nitrogen oxideformation exponentially increases as the flame temperature rises,diffusion combustion generally emits high levels of nitrogen oxides,which is not desirable from the aspect of air-pollution control.

(2) On the other hand, the premixed combustion system is used to lowerthe level of NOx. FIG. 3 shows an example wherein the central portionemploys diffusion combustion having good combustion stability and theouter-periphery side employs premixed combustion having low NOx emissionto lower the level of NOx. In FIG. 3, air 50 sent from a compressor 10passes between an outer casing 2 and a combustor liner 3, and a portionof the air flows into a combustion chamber 1 as cooling air 31 for thecombustor liner and combustion gas in the combustor liner, and anotherportion of the air flows into a premixing chamber 23 as premixedcombustion air 48. Remaining air flows into the combustion chamber 1,flowing through a passage between the premixing-chamber passage and thecombustor end plate and then through a combustion air hole 14 and acooling air hole 17. Gaseous fuel 16 for diffusion combustion isinjected into the combustion chamber 1 through a diffusion fuel nozzle13 to form a stable diffusion flame 4. Premixing gaseous fuel 21 isinjected into the annular premixing chamber 23 through a fuel nozzle 8,being mixed with air to become a premixed air fuel mixture 22. Thispremixed air fuel mixture 22 flows into the combustion chamber 1 to forma premixed flame 5. Generated high-temperature combustion gas is sent toa turbine 18, performs its work, and then is exhausted.

However, if such a premixed combustion system is employed, includedinstable factors peculiar to premixed combustion may cause a flame toenter the premixing chamber and burn the structure, or cause what iscalled a flash back phenomenon to occur.

In an embodiment according to the present invention, a fuel jet passageand a combustion air flow passage are disposed on the same axis to forma coaxial jet in which the air flow envelops the fuel flow, and alsodisposed on the wall surface of the combustion chamber to form multiholecoaxial jets being arranged such that a large number of coaxial jets canbe dispersed. Further, this embodiment is arranged such that a part ofor all of the coaxial jets can flow in with a proper swirling anglearound the combustor axis. Furthermore, it is arranged such that thefuel supply system is partitioned into a plurality of sections so thatfuel can be supplied to only a part of the system during the gas turbinestartup operation and partial loading operation.

In the form of a coaxial jet in which the air flow envelopes the fuel,the fuel flows into the combustion chamber, mixes with an ambientcoaxial air flow to become a premixed air fuel mixture having a properstoichiometric mixture ratio, and then comes in contact with ahigh-temperature gas and starts to burn. Accordingly, low NOx combustionequivalent to lean premixed combustion is possible. At this time, thesection which corresponds to a premixing tube of a conventionalpremixing combustor is extremely short, and the fuel concentrationbecomes almost zero in the vicinity of the wall surface, which keeps thepotential of burnout caused by flash back very low.

Further, by providing an arrangement such that a part of or all of thecoaxial jets flow in with a proper swirling angle around the combustoraxis, in spite of the form of a coaxial jet flow, it is possible tosimultaneously form a recirculating flow to stabilize the flame.

Furthermore, it is possible to ensure the combustion stability bysupplying fuel to only a part of the system during the gas turbinestartup operation and partial loading operation thereby causing the fuelto become locally over-concentrated and burning the fuel in themechanism similar to the diffusion combustion which utilizes oxygen inthe ambient air.

First Embodiment

A first embodiment according to the present invention will be describedhereunder with reference to FIG. 1. In FIG. 1, air 50 sent from acompressor 10 passes between an outer casing 2 and a combustor liner 3.A portion of the air 50 is blown into a combustion chamber 1 as coolingair 31 for the combustor liner 3. Further, remaining air 50 is blowninto the combustion chamber 1 as coaxial air 51 from the interior ofinner cylinder 2 a through air holes 52 in an inner end wall 52 a of theinner cylinder. End wall 52 a is in the form of a disc member.

Fuel nozzles 55 and 56 are disposed coaxially or almost coaxially withcombustion air holes 52. Fuel 53 and fuel 54 are injected into acombustion chamber 1 from fuel nozzles 55 and fuel nozzles 56 throughsupply paths 55 a, 56 a as jets almost coaxial with the combustion airthereby forming a stable flame. Generated high-temperature combustiongas is sent to a turbine 18, performs its work, and then is exhausted.

In this embodiment, with respect to fuel 53 and fuel 54, a fuel supplysystem 80 having a control valve 80 a is partitioned. That is, the fuelsupply system 80 herein is partitioned into a first fuel supply system54 b and a second fuel supply system 53 b. The first fuel supply system54 b and the second fuel supply system 53 b haveindividually-controllable control valves 53 a and 54 a, respectively.The control valves 53 a and 54 a are arranged such that each valveindividually controls each fuel flow rate according to the gas turbineload. Herein, the control valve 53 a can control the flow rate of a fuelnozzle group 56 in the central portion, and the control valve 54 a cancontrol the flow rate of a fuel nozzle group 55 which is a surroundingfuel nozzle group. This embodiment comprises a plurality of fuel nozzlegroups: a fuel nozzle group in the central portion and a surroundingfuel nozzle group, fuel supply systems corresponding to respective fuelnozzle groups, and a control system which can individually control eachfuel flow rate as mentioned above.

Next, the nozzle portion will be described in detail with reference toFIGS. 4(a) and 4(b). In this embodiment, the fuel nozzle body is dividedinto central fuel nozzles 56 and surrounding fuel nozzles 55. On theforward side of the fuel nozzles 55 and 56 in the direction ofinjection, corresponding air holes 52 and 57 are provided. A pluralityof air holes 52 and 57 both having a small diameter are provided on thedisciform member 52 a. A plurality of air holes 52 and 57 are providedso as to correspond to a plurality of fuel nozzles 55 and 56.

Although the diameter of the air holes 52 and 57 is small, it ispreferable to form the holes in such size that when fuel injected fromthe fuel nozzles 55 and 56 passes through the air holes 52 and 57, afuel jet and an circular flow of the air enveloping the fuel jet can beformed accompanying the ambient air. For example, it is preferable forthe diameter to be a little larger than the diameter of the jet injectedfrom the fuel nozzles 55 and 56.

The air holes 52 and 57 are disposed to form coaxial jets together withthe fuel nozzles 55 and 56, and a large number of coaxial jets in whichan annular air flow envelopes a fuel jet are injected from the end faceof the air holes 52 and 57. That is, the fuel holes of the fuel nozzles55 and 56 are disposed coaxially or almost coaxially with the air holes52 and 57, and the fuel jet is injected in the vicinity of the center ofthe inlet of the air holes 52 and 57, thereby causing the fuel jet andthe surrounding annular air flow to become a coaxial jet.

Since fuel and air are arranged to form a large number of small diametercoaxial jets, the fuel and air can be mixed at a short distance. As aresult, there is no mal distribution of fuel and high combustionefficiency can be maintained.

Further, since the arrangement of this embodiment promotes a partialmixture of fuel before the fuel is injected from the end face of an airhole, it can be expected that the fuel and air can be mixed at a muchshorter distance. Furthermore, by adjusting the length of the air holepassage, it is possible to set the conditions from almost no mixtureoccurring in the passage to an almost complete premixed condition.

Moreover, in this embodiment, a proper swirling angle is given to thecentral fuel nozzles 56 and the central air holes 57 to provide swirlaround the combustion chamber axis. By providing a swirling angle to thecorresponding air holes 57 so as to give a swirling component around thecombustion chamber axis, the stable recirculation area by swirl isformed in the air fuel mixture flow including central fuel, therebystabilizing the flame.

Furthermore, this embodiment can be expected to be greatly effective forvarious load conditions for a gas turbine. Various load conditions for agas turbine can be handled by adjusting a fuel flow rate using controlvalves 53 a and 54 a shown in FIG. 1.

That is, under the condition of a small gas turbine load, the fuel flowrate to the total air volume is small. In this case, by supplyingcentral fuel 53 only, the fuel concentration level in the central areacan be maintained to be higher than the level required for the stableflame being formed. Further, under the condition of a large gas turbineload, by supplying both central fuel 53 and surrounding fuel 54, leanlow NOx combustion can be performed as a whole. Furthermore, under thecondition of an intermediate load, operation similarly to diffusingcombustion which uses ambient air for combustion is possible by settingthe equivalence ratio of the central fuel 53 volume to the air volumeflown from the air holes 57 at a value of over 1.

Thus, according to various gas turbine loads, it is possible tocontribute to the flame stabilization and low NOx combustion.

As described above, by arranging a coaxial jet in which the air flowenvelopes the fuel, the fuel flows into the combustion chamber, mixeswith an ambient coaxial air flow to become a premixed air fuel mixturehaving a proper stoichiometric mixture ratio, and then comes in contactwith a high-temperature gas and starts to burn. Accordingly, low NOxcombustion equivalent to lean premixed combustion is possible. At thistime, the section which corresponds to a premixing tube of aconventional premixing combustor is extremely short.

Furthermore, the fuel concentration becomes almost zero in the vicinityof the wall surface, which keeps the potential of burnout caused byflash back very low.

As described above, this embodiment can provide a gas turbine combustorhaving low level NOx emission and good combustion stability and anoperating method thereof.

Second Embodiment

FIGS. 5(a) and 5(b) show the detail of the nozzle portion of a secondembodiment. In this embodiment, there is a single fuel system which isnot partitioned into a central portion and a surrounding portion.Further, a swirling angle is not given to the nozzles in the centralportion and the combustion air holes. This embodiment allows the nozzlestructure to be simplified in cases where the combustion stability doesnot matter much according to operational reason or the shape of thefuel.

Third Embodiment

FIGS. 6(a) and 6(b) show a third embodiment. This embodiment is arrangedsuch that a plurality of nozzles of a second embodiment shown in FIG. 5are combined to form a single combustor. That is, a plurality ofmodules, each consisting of fuel nozzles and air holes, are combined toform a single combustor.

As described in a first embodiment, such an arrangement can provide aplurality of fuel systems so as to flexibly cope with changes of turbineloads and also can easily provide different capacity per one combustorby increasing or decreasing the number of nozzles.

Fourth Embodiment

FIGS. 7(a) and 7(b) show a fourth embodiment. This embodiment isbasically the same as a second embodiment, however, the difference isthat a swirling component is given to a coaxial jet itself by an airswirler 58.

This arrangement promotes mixture of each coaxial jet, which makes moreuniform low NOx combustion possible. The structure of the fuel nozzlewhich gives a swirling component to a fuel jet can also promote mixture.

Fifth Embodiment

FIGS. 8(a) and 8(b) show a fifth embodiment. The difference of thisembodiment is that the nozzle mounted to the central axis of a thirdembodiment is replaced with a conventional diffusing burner 61 whichcomprises air swirlers 63 and fuel nozzle holes 62 which intersect withthe swirlers, respectively.

By using a conventional diffusing combustion burner for startup,increasing velocity, and partial loading in this arrangement, it isconsidered that this embodiment is advantageous when the startingstability is a major subject.

Sixth Embodiment

FIGS. 9(a) and 9(b) show a sixth embodiment. This embodiment has aliquid fuel nozzle 68 and a spray air nozzle 69 in the diffusing burner61 according to the embodiment shown in FIGS. 8(a) and 8(b) so thatliquid fuel 66 can be atomized by spray air 65 thereby handling liquidfuel combustion. Fuel 67 is supplied to the liquid fuel nozzle 68.Although, from the aspect of low level NOx emission, not much can beexpected from this embodiment, this embodiment provides a combustor thatcan flexibly operate depending on the fuel supply condition.

Seventh Embodiment

FIG. 10 shows a seventh embodiment. This embodiment provides anauxiliary fuel supply system 71, a header 72, and a nozzle 73 on thedownstream side of the combustor in addition to a first embodiment shownin FIG. 1 and FIGS. 4(a) and 4(b). Fuel injected from a nozzle 73 flowsinto a combustion chamber as a coaxial jet through an air hole 74, andcombustion reaction is promoted by a high-temperature gas flowing out ofthe upstream side.

Although such an arrangement makes the structure complicated, it ispossible to provide a low NOx combustor which can more flexibly respondto the load.

Eighth Embodiment

FIG. 11 shows an eighth embodiment. In this embodiment, each fuel nozzleof the embodiment shown in FIGS. 9(a) and 9(b) is made double structuredso that liquid fuel 66 is supplied to an inner liquid-fuel nozzle 68 andspray air 65 is supplied to an outer nozzle 81. This arrangement allowsa large number of coaxial jets to be formed when liquid fuel 66 is used,thereby realizing low NOx combustion where there is very littlepotential of flash back.

Furthermore, it can also function as a low NOx combustor for gaseousfuel by stopping the supply of liquid fuel and supplying gaseous fuelinstead of spray air. Thus, it is capable of providing a combustor thatcan handle both liquid and gaseous fuel.

As described above, by making a part of or all of the fuel nozzlesdouble structured so that spraying of liquid fuel and gaseous fuel canbe switched or combined, it is possible to handle both liquid andgaseous fuel.

Thus, according to the above-mentioned embodiment, by arranging a largenumber of coaxial jets in which the air flow envelopes the fuel, thefuel flows into the combustion chamber, mixes with an ambient coaxialair flow to become a premixed air fuel mixture having a properstoichiometric mixture ratio, and then comes in contact with ahigh-temperature gas and starts to burn. Accordingly, low NOx combustionequivalent to lean premixed combustion is possible. At this time, thesection which corresponds to a premixing tube of a conventionalpremixing combustor is extremely short, and the fuel concentrationbecomes almost zero in the vicinity of the wall surface, which keeps thepotential of burnout caused by flash back very low.

This embodiment can provide a gas turbine combustor having low level NOxemission and good combustion stability and an operating method thereof.

Ninth Embodiment

FIG. 12 is a sectional view of a part of the fuel nozzle 55 and acombustion air hole 52 formed in disc member 52 a, arrangedapproximately coaxially. The combustion air hole 52 is provided at adownstream side of the fuel nozzle 55 with respect to a fuel jet flow,that is, a premixing flow passage is formed at the downstream side ofthe fuel jet of the fuel nozzle 55. The size (flow passagecross-sectional area) of the combustion air hole 52 is better to belarger than a cross-sectional area of a fuel jet hole of the fuel nozzle55. In the present embodiment, the diameter (premixing flow passagediameter area) of the combustion air hole 52 is larger than the fuelinjection hole diameter (area) of the fuel nozzle 55. Fuel is jettedfrom the fuel nozzle 55 through the premixing flow passage while airflows through the premixing flow passage, whereby the fuel and airbecome a coaxial jet flow. In this case, it is desirable that the fuelfrom the fuel nozzle 55 is jetted toward a radially central portion ofan inlet of the combustion air hole 52 and a good coaxial jet flow isformed. Further, in the case of the present embodiment, a fuelconcentration distribution at a downstream side of an air outlet issymmetric with respect to a center of the coaxial flow as shown in FIG.12, and the fuel and air rapidly mix with each other and the mixturebecome uniform at the fuel and air run downstream. Thereby, a low NOxperformance equivalent to a conventional premixing combustion system isrealized by a short premixing distance as compared with the conventionalpremixing combustion system.

Further, FIG. 13(a) and FIG. 13(b) each show an example that the axis ofthe combustion air hole 52 is inclined at an angle θ° against the fueljet axis of the fuel nozzle 55. The combustion air hole 52 is arrangedto be coaxial in the vicinity of an inlet thereof but to be inclinedagainst the fuel jet direction. In the case of such an arrangement, adistribution of fuel concentration in a place downstream of the airoutlet is asymmetric with respect to the air jet flow axis as shown inFIG. 13(a). The fuel and air becomes mixed and uniform as the fuel airrun downstream, however the asymmetry does not completely disappear anda concentration difference exists. For example, for coaxial jet holesnear the radial center of a burner or combustor formed of a aggregationof a plurality of coaxial jet holes, as shown in FIG. 13(b), it isconsidered to positively utilize such a deviation between the fuel jetaxis and the air hole axis. That is, in the present embodiment, theburner is constructed so that the above-mentioned inclination (θ°) isprovided for the combustion air holes around a flame stabilizing regionwhich is around a radially central portion of the burner, but theinclination is not provided (θ°=0) for the combustion air holes in theother region than the central portion, whereby it is possible to keepthe fuel concentration of the flame stabilizing region relatively richand make the stability of flame stronger. In the present embodiment, byproviding only the combustion air holes with an angle not parallel tothe axis of the burner such as swirling angle while employing a straightjet hole having no swirling angle or no inward or outward angle, it ispossible to provide premixed gas with a swirling angle or an inward oroutward angle by a relatively simple construction and it is possible toset a premixed gas flow according to the construction and object of theburner, which is excellent.

Next, FIG. 14 is an example in which an axial position of the fuel jethole and combustion air hole is the same as in FIG. 12 and a positionaldeviation (d) in a radial direction is intentionally set therebetween.By the positional deviation, a fuel concentration difference becomes anasymmetric distribution with respect to an axis of air jet flow, wherebyit is possible to positively generate a difference in fuel concentrationand improve combustion characteristics such as combustion stability.

In the present embodiment as mentioned above, fuel from the fuel nozzle55 flows along an approximately central portion of premixed gas in thepremixing flow passage. Further, the burner is constructed so that airfrom an outer peripheral side of the fuel nozzle 55 flows in thepremixing flow passage along an outer peripheral side thereof.Therefore, the air flows at the outer peripheral side of the fuel flowalong the fuel flow in the premixing flow passage, and the fuel and airflows become approximately coaxial. By providing a plurality of nozzlesof such formation, it is possible to promote mixing of fuel and air andrealize stable combustion by a simple construction.

Further, FIG. 15(a) and FIG. 15(b) show an example of a short premixingdistance L and an example of a long premixing distance, respectively.The mixing by rapid expansion after being going out of the combustionair hole is predominant, and it is considered that an influence of thepremixing distance L on the uniformity of mixing and low NOx performanceis not so large. As shown in FIG. 15(a), even if a member forming thecombustion air hole is made thin thereby to make the premixing distanceL short, it is considered that the low NOx performance is sufficientlysecured. On the other hand, saving of the material of the member formingtherein the air hole and a work cost of perforation of the air hole canbe expected, whereby it is an advantage for cost reduction. FIG. 15(b)shows an example in which the premixing distance L is sufficiently long.It can be expected that fuel and air are sufficiently mixed within themixing flow passage, and it is possible to provide a burner excellent inlow NOx performance. Further, in the case where swirling components areprovided by providing an inclination angle for the combustion air holeand a function such as giving an inward or outward deviation angle isprovided, also, the mixing distance L is preferable to be about severaltimes as large as the air hole diameter.

FIGS. 15(c) and 15(d) show an example in which axial distances G betweenan end of the fuel jet hole and an inlet of the air hole are different.FIG. 15(c) shows an example that the axial distance G is large. Thisexample is advantageous in uniform mixing and low NOx performancebecause a substantial premixing distance can be made long. Further,since the length of the fuel nozzle can be made short, a manufacturingperformance of the fuel nozzle is increased and cost reduction ispossible. On the other hand, FIG. 15(d) is an example of an arrangementin which a premixing flow passage is formed at a downstream side of thefuel nozzle 55 and the axial distance G is minus, that is, the fuel jethole projects into inside of the air hole. By such arrangement,potential of backfire can be reduced greatly, and the arrangement isconsidered to be effective in the case where fuel of excellentignitability such as dimethylether (DME) is burnt with low NOx emission.

FIGS. 15(e) and 15(f) show an example in which the diameter D of the airhole 52 is small and an example in which it is large, respectively. Inthe case of FIG. 15(e) in which the diameter D is made small and thenumber of the air holes are increased thereby, fuel and air aredispersed finely and supplied, so that they are mixed well and uniformin a short distance and it is suited for the case where a lower NOxperformance is considered important. In the case where the diameter D ofthe air hole is made large and the number of the air holes is made lessas shown in FIG. 15(f), the mixing distance is necessary to be long andthe uniformity of mixing is lost a little, so that the low NOxperformance is a little inferior to the above, however, it isadvantageous in the case where cost reduction is considered importantbecause working steps are reduced and the required manufacturingprecision is not so high.

Tenth Embodiment

FIG. 16(a) shows another embodiment. In the embodiment described above,the coaxial air holes 52 within a burner plane are arranged coaxiallyand dispersively, however, basic characteristics are not lost even inlattice or zigzag arrangement of the air holes. FIG. 16(a) shows anexample of such an arrangement as mentioned above. In the case of suchan arrangement, axial position at which flame is formed is within asection of the liner and substantially the same floating flames aregenerated although it differs according to an average velocity on aburner liner. It is better on manufacturing because of simpleconstruction, however, in some cases, it is insufficient in flamestability. FIG. 16(b) shows an example for such a case, in which aregion in which pitches between air holes 52 are the same and areas ofthe air holes each are smaller, a region of no air hole or largerpitches, or the like are provided thereby to form a low flow rateportion (low speed portion) and a circulation flow region, wherebyflames are stabilized in those regions. With such a construction,potential of backfire is low, and it is possible to provide a burnerwith both low NOx performance and combustion stability.

FIG. 17 shows an example of experimental results about a relationshipbetween premixing distance L and NOx emission amount in the representinvention. Although complete premixing combustion that fuel and air aremixed completely and then burnt is necessary to use a premixing devicewith sufficiently long mixing distance or large pressure loss, a NOxemission amount by the complete premixing combustion is very small (apoint A in FIG. 17). On the other hand, in a practical premixing deviceconstruction which is constructed by arranging a plurality of fuelnozzles in an annular premixing flow passage, NOx emission amountincreases in an approximately reverse proportion to the premixingdistance L, and an example of NOx emission by such a premixing device isshown by a point B.

On the contrary, in the present invention, a relationship betweenpremixing distance and NOx emission amount in one embodiment of thepresent invention in which the nozzles and air holes are arranged so asto be a plurality of coaxial jet flows is as shown by a point C in FIG.17, low NOx performance equivalent to that by a conventional premixingdevice can be achieved by a premixing distance equal to or smaller than1/20 times as long as the premixing distance in the conventionalconstruction although the low NOx performance is less than the perfectpremixing combustion.

1. A gas turbine combustor having a combustion chamber supplied withfuel and air, comprising: a plurality of fuel nozzles each jetting thefuel; a disc member arranged at a downstream side of said plurality offuel nozzles with respect to fuel jet flows; and a plurality ofpremixing flow passages made of holes formed in said disc member andhaving areas larger than areas of fuel jet holes of said plurality offuel nozzles, respectively; and wherein said plurality of fuel nozzlesjet fuel through said plurality of premixing flow passages,respectively, from an upstream side to a downstream side of saidcombustion chamber.
 2. A gas turbine combustor having a combustionchamber supplied with fuel and air, comprising: a plurality of fuelnozzles each jetting the fuel; a disc member arranged at a downstreamside of said plurality of fuel nozzles with respect to fuel jet flows;and a plurality of premixing flow passages made of holes formed in saiddisc member and having diameter areas larger than diameter areas of fueljet holes of said plurality of fuel nozzles, respectively; and whereinfuel from each of said plurality of fuel nozzles flows in said premixingflow passage along approximately a central portion thereof and the airfrom an outer peripheral side of said fuel nozzle flows in saidpremixing flow passage along the outer peripheral side thereof, and thefuel is jetted from an upstream side to a downstream side of saidcombustion chamber through said premixing flow passages.
 3. A gasturbine combustor comprising: a combustion chamber supplied with fueland air; a plurality of fuel nozzles each jetting the fuel; a discmember arranged at a downstream side of said plurality of fuel nozzleswith respect to fuel jet flows; and a plurality of premixing flowpassages made of holes formed in said disc member and having flowdiameter areas larger than diameter areas of fuel jet holes of saidplurality of fuel nozzles, respectively; and wherein said plurality offuel nozzles each jet fuel to approximately central portions of inletportions of said premixing flow passages from an upstream side to adownstream side of said combustion chamber, respectively.
 4. A method ofoperating a gas turbine combustor having a combustion chamber suppliedwith fuel and air, wherein fuel is jetted from a plurality of fuelnozzles from an upstream side to a downstream side of the combustionchamber through a plurality of holes each being formed in a disc memberand each hole having an area larger than a diameter area of a fuel jethole of each of the plurality of fuel nozzles with the jetted fuel beingmixed with air in the holes.